1. Field of the Invention
This invention relates to a method as well as a punching and scoring tool for production of scored punched parts.
2. Description of the Related Art
Cardboard folding box blanks are usually provided with scores, which give the folding boxes their defined shape when they are subsequently erected. The contours as well as necessary incisions in the folding box blank are produced by punching. Manufacture is by strip steel punching and scoring tools on flat-bed or rotary punches.
The strip steel punching and scoring tools usually consist of a carrier board made e.g. from wood, composites of plastics with glass fabric or reinforced with metal plates in sandwich construction. Slots to receive punching or scoring rules are provided in these carrier boards according to the box contours. The punching rules project exactly as far as or further than the scoring rules from the carrier board. The punching rules operate against a punching plate made in most instances from steel. The scoring rules produce a scoring ridge in the folding box material by forcing the latter into a scoring groove. These scoring grooves can be cut into the punching plate or mounted as an attachment on the punching plate. The scores and punching contours are produced with a single punching stroke in this way, the scores being shaped only when the punching rules have started the punching process. Such tools are described, for example, in patents DE 39 28 916 C1 or DE 38 31 393 A1.
The punching and scoring process is problematical in the already known punching and scoring tools, because the material is drawn into the corresponding scoring groove by the scoring rule only when the punching process has already started, i.e. when the punching rules have already penetrated the cardboard.
As a result of drawing the material into the scoring groove, travel extension of theoretically up to about 50% compared to the scoring groove width is required. The scoring rule attempts to obtain this additional material laterally. However, this is possible only to a limited extent, because the punching rules hold the material firmly. This process is all the more problematical the closer parallel punching and scoring rules are to each other. If the punching rules rest on the material, the latter is fixed, the blade cutting edge drawing in material in the compression phase until the material is finally cut through, so that the material inflow for formation of the scoring ridge is greatly impeded. As not enough material can flow behind, tensile stresses occur at the cutting points, because the scoring rules also attempt to obtain material while they enter the scoring groove. The tensile stresses in the material thus cause the cutting process to become a cutting/tearing process, which has a negative effect on the cutting quality. The scoring ridge is in turn subject to tensile stresses, which are caused by the adjacent cutting rules. As punching and scoring rules are arranged symmetrically in a folding box blank only in exceptional cases, the tensile stresses acting on the scoring ridge are usually asymmetrical, which leads to asymmetry or inclination of the scoring ridge according to the distance from the adjacent rules and greatly impairs the folding behaviour. The limits of the punchability and scorability are consequently predetermined according to the punched material and the folding box geometry. In particular the quality of the scoring ridge is of crucial importance for the subsequent folding processes in high-speed folding box gluing and packing machines.